Accelerating vulcanization with benzothiazole-2-sulfinamides



United States Patent.

3,541,060 ACCELERATING VULCANIZATION WITH BENZOTHIAZOLE-Z-SULFINAMIDES Alan Jeffrey Neale and Terence James Rawlings, Llangollen, Wales, assignors to Monsanto Chemicals Limited, London, England, a British company No Drawing. Original application June 1, 1967, Ser. No. 642,717, now Patent No. 3,454,590, dated July 8, 1969. Divided and this application Dec. 18, 1968, Ser. No.

Int. Cl. C0815 27/06; C07d 91/44 U.S. Cl. 260-795 6 Claims ABSTRACT OF THE DISCLOSURE Vulcanization accelerators are benzothiazole-2-sulfinamides of the formula where R and R are each an aliphatic or cycloaliphatic group of 2-20 carbon atoms or R and R are linked to form a saturated cyclic system with the nitrogen atom.

BACKGROUND OF THE INVENTION This application is a division of application Ser. No. 642,717 filed June 1, 1967, now U.S. Pat. 3,454,590.

The invention pertains to new compounds useful as vulcanization accelerators for rubber and processes for making the compounds. The applicable U.S. patent classifications are 260-3066 and 260-779.

The compounds of this invention are delayed-action accelerators, i.e., an increase in scorch time is shown in vulcanizing rubber and using the compounds of this invention. Mingassons U.S. Pat. 2,585,155 (Cl. 260-3066) 1952, assigned to Societe Anonyme de Matieres Colorantes et Produits Chimiques Francolor, Paris, France, a French a company, discloses N,N-dimethylbenzothiazole-2-sulfinamide as a vulcanization accelerator. The benzothiazole-2- sulfinamides of this invention show greater degree of delayed action than N,N-dimethylbenzothiazole-Z-sulfinamide.

SUMMARY OF THE INVENTION where R and R are each an aliphatic or cycloaliphatic group or where R and R are linked to form a saturated cyclic system with the nitrogen atom.

New compounds that can be produced by the process are benzothiazole-Z-sulfinamides where R and R in the above formula each represent an aliphatic or cycloaliphatic group and the total number of carbon atoms in R and R is at least four, and sulfinamides where R and R are linked to form a saturated cyclic system with the nitrogen atom.

The invention includes a process in which a new compound as defined above is employed as an accelerator for the vulcanization of rubber.

Sulfinamides that can be produced by oxidation of the corresponding sulfenamides in the process defined above can also be obtained by reaction of a benzothiazole-2- sulfinyl halide with an appropriate amine. In particular, sulfinamides in which the sulfinamide grouping is represented by the formula:

0 R i-N can be obtained by reaction of the sulfinyl halide with an amine having the formula HNRR. This process for the production of a benzothiazole-Z-sulfinamide comprises the reaction of a benzothiazole sulfinyl halide with ammonia or an amine. The compound 2-morpholino-sulfinylbenzothiazole prepared by this process is a useful accelerator. The compound is claimed in the copending application of Robert H. Campbell and Alfred B. Sullivan, Ser. No. 642,712, filed June 1, 1967.

The oxidation process of the invention can be applied to the production of benzothiazole-Z-sulfinamide itself and also to the production of sulfinamides in which the nitrogen atom carries a single substituent, for example N-alkyl and N-cycloalkyl benzothiazole-Z-sulfinamides. In the sulfinamides where the nitrogen atom is doubly substituted as shown in the above formula, the aliphatic groups from which R and R can be selected include alkyl groups, generally those containing from 1 to 20 carbon atoms having either straight or branched chains, and more especially alkyl groups containing from 2 to 12 carbon atoms, for example ethyl, isopropyl, sec.-butyl, n-amyl, hexyl, octyl, nonyl, and dodecyl groups. R and R may also be selected from substituted alkyl groups, for example halogen, cyano, or aryl-substituted alkyl groups such as for instance cyanoethyl and benzyl.

Where a group R and R is cycloaliphatic, it is usually one containing from 5 to 7 carbon atoms in the ring. The preferred groups are cycloalkyl and alkylcycloalkyl groups, for example cyclopentyl, cyclohexyl, or methylcyclohexyl,

although substituents, as exemplified above for instance,.

may be present.

Instances of benzothiazole sulfinamides where R and R are linked and form a saturated cyclic system with the nitrogen atom, are those in which NRR' represents a piperidino or substituted piperidino group, or a hexamethyleneimino group.

The benzothiazole-Z-sulfinamides that can be produced by the process of the invention include, moreover, members where the benzene nucleus carries one or more substituents. Such a substituent can be, for example a halogen atom, especially chlorine or bromine, a nitro group, an alkyl group, or an alkoxy group.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of benzothiazole2-sulfinamides that can be obtained by the process of the invention are:

N-methyl-N-cyclohexyl benzothiazole-2-sulfinamide N,N-diisopropyl benzothiazole-Z-sulfinamide N,N-diisobutyl benzothiazole-2-sulfinamide N,N-dicyclohexyl benzothiazole-Z-sulfinamide 2-hexamethyleneiminosulfinylbenzothiazole N,N-diisopropyl-6-chlorobenzothiazole-Z-sulfinamide, and N,N-dicyclohexyl-6-ethoxybenzothiazole-2sulfinamide.

In practice, the oxidation process of this invention is usually conducted by adding the aqueous solution of alkali metal hypohalite to a dispersion or solution of the benzothiazole sulfenamide in an inert liquid dispersion or solvent medium. This can be water but is preferably a watermiscible organic solvent. Water-miscible solvents that can be used include alcohols, ketones, glycols and dioxane, the alcohols, especially methanol, being generally preferred.

Preferred reaction temperatures for the oxidation are within the range 30 to 80 C. The optimum depends on the particular benzothiazole-Z-sulfenamide that is oxidized, but is often within the range 35 to 50 C. When using methanol as the water-miscible solvent, it is sometimes convenient to conduct the process under reflux at the boiling point.

The hypohalite is employed in at least the stoichiometric quantity required for oxidation of the sulfenamide to the sulfinamide, but not usually in amounts exceeding three times this quantity. Good results are obtained using from 1.5 to 2.5 moles of hypohalite per mole of sulfenamide. Sodium hypochlorite is the alkali metal hypohalite normally employed in practice, although hypochlorites of other alkali metals, for instance potassium and lithium, and the alkali metal salts of other hypohalous acids, for instance hypobromous acid, are functionally satisfactory. The commercial aqueous solution of sodium hypochlorite containing nominally about 15% by weight NaOCl (in practice usually from 12 to 16% by weight) is quite suitable and is in fact preferred to more dilute solutions.

The benzothiazole-Z-sulfinyl halides, which have not hitherto been described and are useful in the second process of the benzothiazole-2-sulfinamides of this invention, can be obtained by the reaction of a thionyl halide with an alkyl benzothiazole-2-sulfinate. Benzothiazole-Z-sulfinyl chlorides, for example, are obtained in high yield by the action of thionyl chloride on lower alkyl benzothiazole-2- sulfinates, particularly methyl benzothiazole-2-sulfinates.

For the conversion of the benzothiazole sulfinyl halide to the required benzothiazole. sulfinamide, it is convenient to use a sufficient excess of ammonia or the amine for the excess base to function as a hydrogen-halide acceptor. The reaction proceeds at ordinary atmospheric temperatures, for example from 5 to 25 C., although somewhat higher temperatures, for example up to 60 C. can be used if desired. While an inert diluent may facilitate the reaction and the isolation of the product, its presence is not essential. Inert diluents that can be used include hydrocarbons, particularly aromatic hydrocarbons such as for instance benzene, and halogenated hydrocarbons.

The new compounds can be used as accelerators in the vulcanization of natural and synthetic sulfur-vulcanizable rubbers. Synthetic rubbers that can be vulcanized include polymers of 1,3-butadienes, for instance of 1,3-butadiene itself and of isoprene, copolymers of 1,3-butadienes with other monomers, such as styrene, acrylonitrile, isobutylene, or methyl methacrylate, and polyolefin rubbers, for instance ethylene-propylene terpolymers.

In the vulcanization process, the accelerators are usually used in conjunction with sulfur or a sulfur-containing vulcanizing agent, for example an amine disulfide or thiuram sulfide, and with other commonly used ingredients, for example zinc oxide, stearic acid, a filler and an antioxidant.

The additives can be incorporated into unvulcanized rubber by conventional means, using for example an internal mixer or a roll mill, or by adding a solution or suspension to a rubber latex, giving a mixture which is subsequently vulcanized at an elevated temperature. This temperature is one that is appropriate to the particular rubber concerned, for example a temperature in the range 135 -l55 C. where the composition is based on natural rubber, or a temperature in the range of l40l60 C. where the composition is based on a styrene-butadiene rubber.

The amount of accelerator used depends on a number of factors, including for example the type of rubber and the use for which the vulcanized product is required. The amount is, however, usually within the range 0.3 to 5 parts by weight, and more especially within the range 0.3 to 2 parts by weight, per parts by weight of rubber, for example 0.5, 1.0 and 1.5 parts by weight.

Conventional amounts of other additives referred to above can be used.

The invention is illustrated by the following examples:

EXAMPLE 1 This example describes the production of N,N-dicyclohexylbenzothiazole-Z-sulfinamide by oxidation of N,N-dicyclohexylbenzothiazole-2-sulfenamide using sodium hypochlorite.

150 grams of a 15% by weight aqueous solution of sodium hypochlorite containing 0.3 mole of NaOCl were gradually added during a period of 10 minutes to a suspension of 48.3 grams (0.15 mole) of N,N-dicyclohexylbenzothiazole-Z-sulfenamide in 300 ccs. of bOiling methanol. Boiling was continued for one hour, and then the mixture was cooled to 0 C. By filtration, there were recovered 64 grams of a brown solid, most of which was extracted into benzene leaving 16 grams of insoluble material. The benzene solution was washed thoroughly with water and then dried using sodium sulfate. The benzene was removed at 50 C. in vacuo to give 40 grams of a brown oil which solidified on standing. Crystallization of this solid from ethanol gave 26 grams of unchanged N,N-dicyclohexylbenzothiazole-Z-sulfenamide. The ethanolic mother liquors were evaporated giving a brown oil which on crystallization from 60-80 petroleum ether yielded 5.5 grams of N,N-dicyclohexylbenzothiazole-2-sulfinamide in the form of fawn crystals with a melting point between and 137 C.

EXAMPLE 2 This example describes the production of N,N-dicyclohexylbenzothiazole-2-sulfinamide from benzothiazole-2- sulfinyl chloride and dicyclohexylamine.

2.9 grams (0.0135 mole) of methyl benzothiazole-2- sulfinate were added quickly to 1.6 grams (0.0135 mole) of freshly distilled thionyl chloride. After 30 minutes at room temperature, benzothiazole-Z-sulfinyl chloride had formed as a homogeneous liquid, and was dissolved in 10 cos. of dry benzene. This benzene solution was added gradually to a stirred, cooled solution of 12.2 grams (0.0675 mole) of dicyclohexylamine in 10 cos. of dry benzene. After a further 10 minutes at room temperature the mixture was filtered, the filtrate was washed thoroughly with water and was then dried by standing over anhydrous sodium sulfate. The benzene was removed at 40 C. under reduced pressure leaving 8.9 grams of an oil which crystallized from 60-80 petroleum ether to give 1.8 grams of a solid having a melting point of 1l0-127 C. Recrystallization from a mixture of petroleum ether and benzene using charcoal to decolorize the solution gave 0.6 gram of N,N-dicyclohexylbenzothiazole-2-sulfinamide as colorless crystals having a melting point of 135-136.5 C.

EXAMPLE 3 This example describes the oxidation of N,N-di-isopropylbenzothiazole-Z-sulfenamide to N,N di-isopropylbenzothiazole-Z-sulfinamide using sodium hypochlorite.

grams of a 15% by weight solution of sodium hypochlorite containing 0.25 mole of NaOCl were slowly added to a suspension of 39.6 grams (0.15 mole) of N,N-di-isopropylbenzothiazole-Z-sulfenamide in 300 ccs. of methanol at 40-45 C. The addition was completed in twenty minutes, external cooling being required to keep the temperature within the stated range. After a further ten minutes the product was cooled to 0 C. and extracted with benzene. By evaporation of the solvent from the benzene extracts, there were obtained 33 grams of an oil which was crystallized from petrol-benzene to A masterbatch of the following composition was prepared by compounding on a mill:

give 6.5 grams of N,N-di-isopropylbenzothiazole-Z-sul- Parts by finamide as a white solid with a melting point of 78 i ht; 80 C. (C H N OS requires: C, 55.3; H, 6.42; N, 9.92;

s, 22.7. Found: 0, 55.2; H, 6.41; N, 10.7; s, 23.2%. 5 glnokedfheets 100 Inc oxide 5 EXAMPLE 4 Stearic acid 3 This example describes the production of N,N-di-iso- HAF black 50 propylbenzothiazole-2-sulfinamide from benzothiazole-2- Process 011 3 sulfinyl chloride and di-isopropylamine. Sulfur Benlothiazole'z'sulfinyl chloride Was P p y Each test compound was then incorporated into a sepail'lg grams {0-0135 mole) of methyl'benlothialole-zrate portion of the masterbatch at a level equivalent to sulfinate, to 1.6 grams (0.0135 mole) of freshly distilled 0.5 art per 100 parts by weight of rubber. A second thionyl de. After 30 minut s a 10 In mpe ature series of mixtures was prepared by incorporating each a homogeneous llqllld has been fofmfid a ii q test compound into a separate portion of the masterbatch in 10 Of y benzene, Was Slowly added to a stirred; at a level equivalent to 1.0 part per 100 parts by weight Cooled $0 111tiQI1 of 6.32 grams mole) of of rub r. The mixtures were allowed to stand at room P py 10 of y bfinzene- After a further temperature for 24 hours befor being tested. ten minutes at I'OOIII temperature the mixture was filtered. In one test method a sample under test was placed in The filtrate Was thoroughly Washed With dried a Mooney plastometer fitted with a large rotor, according using sodium Sulfate, and then y p d at in to British Standard Specification No. 1673. The time vacuo to give 43 grams of an Y cfystallilatiwl 0f taken for the reading of the instrument to react 5 units the Oil from Petrol-benzene, p py Z above the minimum at a temperature of 121 C. was rezole-2-sulfinamide was obtained as a colorless crystalline d d as a measure f th scorch ti h hi h thi Solid having a melting Point of Recfystallilafigure, the greater the degree of delayed action of the tion raised the melting point to 82-83.5 C. k t

( 13 1s 2 2 requires! 22.7. In a second test method, cure time and modular Found: 10.3; S, properties of the vulcanizate were measured using the EXAMPLE 5 Monsanto Oscillating Disk Rheometer described by Decker, Wise and Guerry in Rubber World, December P example descflbes the Pmduchfm of 1962, page 68. Cure time was recorded as the time in PhPImOSHIfiHYIbenZOthIaFOIe the of minutes to reach 90% of the maximum cure, and the thlazole'zsulfinyl chlonde Wlth P 1 maximum torque in inch/ pounds was recorded as a meas- Benzothiazole-Z-sulfinyl chloride was first prepared we of the modulus by the rapid Pddmon of 2 grams 5 mole) of A similar series of tests was carried out in styrenemethylbenzothlazole'z'sulfinate to grams (Q0135 butadiene rubber, using a masterbatch having the followmole) of freshly distilled thionyl chloride, allowing the ing composition; mixture to stand at rom temperature for 16 hours, and Parts b then subjecting the reaction mixture to reduced pressure 40 i h at 35 C. to remove methyl chlorosulfite.

5.8 grams (0.0675 mole) of morpholine were added SFyrenePutadwne rubber 100 ,to the residual solid. Gentle warming initiated the reac- Zmc 9 4 tion which was then allowed to proceed at room tempera- Steam: i 2 ture for three days. The reaction mixture was extracted Process. 011 8 with benzene, and the benzene extracts were washed HAF carbon black so thoroughly with water. After drying over sodium sulfate, Sulfur 2 the benzene was removed in vacuo to give 3.1 grams The test compounds were incorporated at a level equiof a yellow oil which was then crystallized from ethanol valent to 1.0 part by weight per 100 parts by weight of to give 0.43 gram of 2-morpholinosulfinylbenzothiazole rubber. For these mixtures the Mooney plastometer was as colorless crystals having a melting point of 101 operated at a temperature 135 C. and the rheometer 102 C. (C H N O2 req ir 4.51; N, at a temperature of 153 C.

10.4; S, 23.9%. Found: C, 49.0; H, 4.57; N, 10.4; S, The results of the various tests described above are 24.4%.) given in the table below:

Natural rubber Accelerator at 0.5 phr. Accelerator at 1.0 phr. Styrene-butadiene rubber Scorch Cure Modulus Scorch Cure Modulus Scorch Cure Modulus N,N-dlisopropyl-benzothiazole-2-sulfinamide. 38 42% 71% 31 32 82 45 50% 74 N,N-diisopropyl-benzothiazole-2-sulfenamide 33% 35 75% 30 27 86 50 44 77 N,N-dimethyl-benzothiazole-2-sulfinamide 26 33 72 23 25 85% 33 35% 71 N,N-dicyelohexyl-benzothiazole-Mulfinamide 38% 42 68 34% 31% 79 53% 54 68 N ,N-dicycIohexyl-benzothiazo1e-2-sulienamide. 34% 41% 71% 28% 29 82 49 45 74 EXAMPLE 6 The results show the generally greater degree of delayed This example describes the production of rubber action of the benzothiazole sulfinamides of the invention canizates using the compounds described in the previous examples as vulcanization accelerators, and includes for comparison results obtained using the corresponding sulfenamides and using N,N-dirnethylbenzothiazole-Z-sulfinamicle in comparison with the corresponding sulfenamides and in comparison with N,N-dimethylbenzothiazole-Z-sulfinamide. The figures for the cure rates and moduli of vulcanizates using the new accelerators represent high degrees 75 of accelerator activity.

It is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

We claim:

1. A process for the vulcanization of a sulfur-vulcanizable rubber, in which an effective amount of a benzothiazole-Z-sulfinamide is employed as a vulcanization accelerator of the formula where 2. The process of claim 1 where R and R with the nitrogen are N,N-diisopropylamino.

3. The process of claim 1 where R and R nitrogen are N,N-dicyclohexylamino.

4. The process of claim 1 where R and R nitrogen are N-methyl-N-cyclohexylamino.

5. The process of claim 1 where R and R nitrogen are N,N-diisobutylamino.

6. The process of claim 1 where R and R nitrogen are hexamethyleneimino.

with the with the with the with the References Cited UNITED STATES PATENTS 2,585,155 2/1952 Mingasson 260-79.5

JOSEPH L. SCHOFER, Primary Examiner C. A. HENDERSON, JR., Assistant Examiner U.S. Cl. X.R.

CER'Y.11*I(.A'FE OF CORRECTJLON Patent No. 3,541,060 Dated November 17, 1970 Inve tofls) Alan J. Neale and Terence Rawlings It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, Column 1, line 10, after "784, 897" add:

- Claims priority, application Great Britain, June' 17,

Signed and sealed this 25th day of May 1971.

r (SEAL) 1 Attest:

' JR .-FLETCHER JR. WILLiAM E. SCHUYLER,

Officer Commissioner of Patents 

